Quasi-equilibrated temperature programmed desorption and adsorption: A new method for determination of the isosteric adsorption heat

Temperature programmed desorption and adsorption (TPDA) studied under quasi-equilibrium conditions using typical flow TPD setup equipped with a chromatographic TCD detector has been found a good method of obtaining the equilibrium data characterizing adsorption of n-hexane on high silica HZSM-5 and HY zeolites. The equilibrium control of sorption has been confirmed by linearity of the isosters constructed from the TPDA profiles. For HZSM-5 it was corroborated by very good agreement obtained in fitting the experimental data with the model based on the dual site Langmuir (DSL) adsorption function. The values of the adsorption enthalpy and entropy, either determined from the adsorption isosters or as the fitted model parameters, were close to the literature data. Increase of the isosteric adsorption heat of hexane with coverage was observed for both zeolites (72–90 kJ mol−1 for HZSM-5 and 46–61 kJ mol−1 for HY).